1. Field of the Invention
The present invention pertains to the reading of indicia having parts of different reflectivity, such as barcode symbols, and more particularly, to a reader for reading indicia which is integrated into either a keyboard or a monitor. The invention has a particular application in reading barcode symbols in instances where there is a need to save space or where there is a need to avoid the cost of purchasing a separate reader component.
2. Description of Related Art
Various optical readers and scanning systems have been developed for reading barcode symbols appearing on a label or the surface of an article. The barcode symbol itself can be a coded pattern of indicia comprising a series of bars of various widths spaced apart from one another to bound spaces of various widths, the bars and spaces having different light-reflecting characteristics. The readers and scanning systems electro-optically transform the graphic indicia into electrical signals, which are decoded into alphanumerical characters intended to be descriptive of the article or some characteristic of it. Such characters typically are represented in digital form and utilized as an input to a data processing system for applications in point-of-sale processing, inventory control and other applications. Scanning systems of this general type have been disclosed, for example, in U.S. Pat. Nos. 4,251,798; 4,360,798; 4,369,361; 4,387,297; 4,409,470 and 4,460,120, all assigned to the assignee of the present invention and incorporated herein by reference.
One embodiment of such a scanning system, as disclosed in some of the above patents, resides in, inter alia, a hand-held, portable laser scanning head supported by a user. The scanning head is configured to enable the user to aim the head at a target to emit a light beam toward a symbol to be read. In another embodiment, the scanning system is a generally bigger and separate workstation, which communicates with a data processing unit. For example, U.S. Pat. No. 4,369,361 discloses such a system and is assigned to the assignee of the present invention and is incorporated herein by reference.
The light source in a laser scanner is typically a gas or semiconductor laser. Use of semiconductor devices as the light source in scanning systems is particularly desirable because of its small size, low cost and low power requirements. The laser beam is optically modified, typically by a lens, to form a beam spot of a certain size at the target distance. In the one embodiment, the beam spot size at the target distance is approximately the same as the minimum width between regions of different light reflectivity, i.e., the bars and spaces of the symbol.
The barcode symbols are formed from bars or elements typically rectangular in shape with a variety of possible widths. The specific arrangement of elements defines the character represented according to a set of rules and definitions specified by the code or "symbology" used. The relative size of the bars and spaces is determined by the type of coding used, as is the actual size of the bars and spaces. The number of characters per inch represented by the barcode symbol is referred to as the density of the symbol. To encode a desired sequence of characters, a collection of element arrangements is concatenated together to form the complete barcode symbol, with each character of the message being represented by its own corresponding group of elements. In some symbologies, a unique "start" and "stop" character is used to indicate where the barcode begins and ends. A number of different barcode symbologies exist. These symbologies include UPC/EAN, Code 39, Code 128, Codabar, and Interleaved 2 or 5, among others.
In order to increase the amount of data that can be represented or stored on a given amount of surface area, several new barcode symbologies have recently been developed. One example of such a symbology is known as two-dimensional (2D) symbology and is discussed in detail in commonly assigned U.S. Pat. Nos. 5,243,655 and 5,304,786, which are incorporated herein by reference. Briefly, that symbology involves a variable number of component symbols of "code words" per row of a nonvolatile electro-optical read-only memory imprinted on a substrate. Code words in alternating rows are selected from mutually exclusive subsets of a mark pattern, the subsets being defined in terms of particular values of discriminator function which is illustrated in the referenced patents as being a function of the widths of bars and spaces in a given code word.
In the scanning systems known in the art, the light beam is directed by a lens or similar optical components along a light path toward a target that includes a barcode symbol on the surface. The scanning systems function by repetitively scanning the light beam in a line or series of lines across the symbol. The scanning component may either sweep the beam spot across the symbol and trace a scan line across the symbol or scan the field of view of the scanner, or do both.
Scanning systems also include a sensor or photodetector, which functions to detect light reflected from the symbol. The photodetector is therefore positioned in the scanner or in an optical path in which it has a field of view, which extends across and slightly past the symbol. A portion of the reflected light which is reflected off the symbol is detected and converted into an electrical signal. Electronic circuitry or software thereafter decodes the electrical signal into a digital representation of the data represented by the symbol that has been scanned. For example, the analog electrical signal from the photodetector may typically be converted into a pulse width modulated digital signal, with the widths corresponding to the physical widths of the bars and spaces. Such a signal is then decoded according to the specific symbology into a binary representation of the data encoded in the symbol, and to the alphanumeric character so represented.
The decoding process in known scanning systems usually works in the following way. The decoder receives the pulse width modulated digital signal from the scanner, and an algorithm implemented in software attempts to decode the scan. If the start and stop characters and the characters between them in the scan were decoded successfully and completely, the decoding process terminates and an indicator of a successful read such as a green light and/or an audible beep is provided to the user. Otherwise, the decode receives the next scan, performs another decode attempt of that scan, and so on, until a completely decoded scan is achieved or no more scans are available.
Decoding 2D symbology is discussed particularly and shown in various flowcharts set forth in the 2D symbology patents incorporated by reference and above identified.
More sophisticated scanning, described in U.S. Pat. No. 5,235,167, assigned to the assignee of this invention, and incorporated herein by reference, carries out selective scanning of 1-D and 2-D barcodes. Preliminary information, such as the barcode type and size, is first decoded during an aiming mode of operation when a relatively narrow and visible raster pattern is impinged on the target. Based upon the preliminary information received by the scanner in the form of light reflected from the target, converted to an electrical signal and decoded, an appropriately sized raster scan pattern is generated. If the barcode pattern is found to be skewed or misaligned with respect to the direction of the raster scanning pattern, the pattern is generated with an orientation in alignment with the barcode.
Another type of barcode reader performs an omni-directional scan. For example, U.S. Pat. No. 5,481,099, assigned to the assignee of the present invention and incorporated herein by reference, shows a scanner for reading indicia having portions of differing light reflectivity which has a means for directing a light beam from the scanner towards the indicia and collecting reflected light returning from the indicia. The scanner includes a scanning arrangement with a scanner component, such as a mirror. First and second vibratory means support the scanner component for angular oscillatory movement to scan the light beam in first and second orthogonal scan directions. The scanning arrangement includes read-start means for moving the scanner component to simultaneously scan the light beam in the first and second scan directions. Control means, operatively connected to the read-start means, are provided for imparting differing signals to the read-start means to (1) alternatively drive fast and slow vibrations of the first and second vibratory means to vary the scanning of the light beam in the first scan direction and (2) to drive vibration of only the second vibratory means to cause the scanning of the light beam in the second scan direction. The scanning of the light beam in the first and second scan directions generates a scan pattern over the indicia.
Another type of barcode reader is one which incorporates an imaging sensor, such as a charge coupled device or other solid state imaging device. Examples of such a reader are shown in U.S. Pat. Nos. 5,672,858 and 5,591,952, assigned to the assignee of the present invention and incorporated herein by reference.
CCDs consist of an array of many detectors, commonly referred to as "pixels." The entire symbol is flooded with light from the reader or ambient light, and each pixel is sequentially read out to determine the presence of a bar or a space. Such readers are light-weight and easy to use, but require substantially direct contact or placement of the reader on the symbol to enable the symbol to be properly read. Such a physical contact of the reader with the symbol is preferred mode of operation for many applications, or as a matter of personal preference by the user.
A basic figure of merit in scanning CCD arrays is a so-called "pixels per module" detection. If detection capability fall below such a figure of merit, scanning cannot proceed since requisite sensitivity is not present.
As noted above briefly, one type of a scanning system is a separate scanning workstation that communicates with a data processing unit. As shown in U.S. Pat. No. 4,369,361, the workstation can take up a significant amount of working space. Also, the workstation can take up an additional port space on the data processing unit. Of course, there are situations where space is at a premium or cannot be spared. In such situations, an additional scanning workstation can cause great inconvenience or cannot be used. Additionally, the workstation can necessitate additional costs: purchasing and maintenance costs, for example. There is a need for an improved scanning system that overcomes the above noted shortcomings.